Along with the rapid development of science and technology, electronic instruments and the miniaturization of electronic equipment are placing higher and higher demands on the characteristics of secondary batteries. From its combined characteristics, lithium ion secondary batteries have the highest development and application potential and very good characteristics as secondary batteries. A widely used battery type in the market place is the cylindrical lithium ion secondary battery made from belt-shaped positive and negative electrodes, and a separator all rolled into a cylindrically-shaped core and encased in a battery shell; or, a belt-shaped positive electrode, negative electrode, and separator all rolled into a cylindrically-shaped core and flattened and inserted in to a rectangular shaped battery shell forming a rectangular-shaped lithium ion secondary battery. However, the problem with this type of structure for a rectangular lithium ion secondary battery is that its space usage efficiency is low.
When compared to other secondary batteries, the internal resistance of lithium ion batteries is higher. Thus the voltage rapidly decreases during high discharge, the discharge time greatly shortens, and the battery capacity highly decreases. As commonly known, the low conductivity of the electrodes is one of the primary reasons the internal resistance of a lithium ion secondary battery may be high. Currently, most of the commercial lithium ion secondary battery uses single or multiple conductors (also called current collectors) as the method for current conduction. But this method of current charge and discharge is limited to a few welding points, where conductibility is low and the current is unevenly distributed in the charging and discharging process.
Thus, the important questions in improving the characteristics of lithium ion batteries are how to effectively use the internal space of the battery shell, how to reach high battery capacity density, how to decrease the battery's internal resistance, and how to improve the large current discharge characteristic of the lithium ion secondary battery.